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Learning Electronics?

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radiance88 - 10-2-2015 at 09:17

Both readings are near the bottom of their respective scales, and the accuracy may be rather poor at that point. What happens if you unplug the transformer with the meter still connected in the circuit? Do the values change, or stay where they are?

I have, on more than one occasion, accidentally tried to measure voltage while the meter was set up to measure current. What happens at this point, is that a lot of current will try to flow through the meter. This blows the protection fuse inside the meter. The voltage measurements are still good, but the meter will not measure current until the fuse is replaced. Sometimes, there is an extra fuse inside the cover, because everyone makes this mistake at some point. Just popping the cover off the back of the meter and looking at the fuse should tell you if this is the problem. Heck, you can even take the fuse out and check it with your ohmmeter. It should be almost 0 ohms.

The only other thing I can think of, is that perhaps one-half of the bridge circuit is not making a good connection. You could try measuring DC current to see if you get a stable reading.

[Edited on 2-9-2015 by WGTR]

I'm almost completely certain that the unit is defective. When I unplug the transformer while keeping the meter connected, it drops down to zero like it should. The conversion factor isn't even correct between milliamps and microamps - those are separated by a factor of a thousand, but according to my multimeter darn near everything measured via the millamp setting is reflected just by a single decimal point nudge to the right with the same number using the microamp setting. I've built several different circuits with different values of resistance and it never even comes close.. Not to even the right decimal point according to the correct computation that Ohm's law gives me.

The funny thing is, I bought this thing not knowing a single thing on how to use it. Now that I've used it frequently, testing different things, I'm not as ignorant anymore and at least have a solid idea as to what figures it should give me. It's been almost a month now though, so I doubt the store will give me a replacement. Ahh the cost of my ignorance.

I checked the fuses and they are both fine. Neither of them blew on me. I see a few reviews on amazon regarding this tool, and seeing some of the defective unit complaints, I think it's feasible that I have been given a dud somehow.

I'm heading to the store first thing tomorrow and going to see if they can give me a replacement, if not fix it. This MM is only 50 USD, but cost me 100 on the other side of the world.

[Edited on 10-2-2015 by radiance88]

radiance88 - 11-2-2015 at 07:59

I took the multimeter to the store with my breadboard setup, and slowly explained to the staff the the DMM wasn't reading my amps properly. I had to teach them about Ohm's Law (lol) and then finally after a bunch of wasted time on both ends, they finally gave me a refund. I didn't exactly want a refund, but they didn't have any other medium-price DMM with autoranging and ability to measure temperature.

They wanted me to upgrade to a Fluke, but I wasn't all that keen on spending half my month's salary all on a single DMM.

I hoofed my way all around town and couldn't find anything decent. So now I'm just a tad bit sad as I've gotten quite used to having it on hand 24/7. I feel naked.. and alone, not having her by my side.

Does anyone have a recommendation for a medium-price DMM (up to $100 USD) that I could buy online? I'm tired of the jacked-up local prices and the hassle of trying to find something that most stores around here don't have.

Sulaiman - 11-2-2015 at 10:13

I use Fluke etc. for work,
but at home I use one of those super cheap (£2.99) DMM a lot
and a £9.99 DMM that has a serial interface.
Both have a temperature range.

With modern components the accuracy and reliability of these cheap DMMs is pretty good.
e.g. my £2.99 DMM when checked against a calibrated Fluke DMM was within it's specified accuracy tolerance.

Personally I'd rather have two (or more) cheap DMM than one expensive DMM.

My only concern is with higher voltages,
I literally exploded one of the cheap DMMs because I (stupidly) assumed that since there was a 2000V dc range,
the meter could measure up to 2000 V ... WRONG !
I trust them up to 240 Vac or about 500 V dc ... after that I'd be very careful, especially in a high power or energy circuit.

P.S. if you do buy an expensive DMM check how much the internal fuses cost to replace
... more than either of my cheap DMMs !

P.P.S. my Fluke uses 4x AA alkaline batteries and it EATS them
my cheap DMM uses a 9V battery and I forget when I last replaced it.

[Edited on 11-2-2015 by Sulaiman]

[Edited on 11-2-2015 by Sulaiman]

Fulmen - 11-2-2015 at 10:18

I agree, even cheap MMs work fine in my experience. I now have 3 (one fluke and two cheap ones) and wouldn't be without any of them, nice for measuring both voltage and currents at the same time. If you find an affordable one with auto-range, go for it.

Magpie - 11-2-2015 at 10:30

I have a cheap RadioShack multimeter that I bought ~10 years ago. It has a plug-in attachment for measuring current via clamp-on. It's OK except it does not measure small resistances (0-1000Ω) accurately. For that I use my 45 year-old Heathkit multimeter which works just fine, but has no current measuring capability. And it is big and clunky.

The Volatile Chemist - 13-2-2015 at 08:52

I'd have a nice one to use, but I took my Dad's analog one apart, which ended up shattering the selection dial in it when I was 10....
Interesting side note, a 'dial' is an organic molecule containing two aldehyde groups....

WGTR - 15-2-2015 at 12:53

Quote:

I want to thank you for helping me so far with my electronics projects. I'd also like to ask you for some advice (being that it probably isn't that important enough to actually post about

Is "true rms" really important in a multimeter? I'm kind of going nuts here trying to find the right DMM for me but I'm not too sure what to look for, and there are so many features, price points that it's kind of weighing on me heavily.

I just want to buy something that will work for my hobbyist stuff, but am not sure that it justifies spending $300 on it either..

You're welcome; no problem.

The answer to your question is subjective, and different people will have different opinions. My personal meter is a Fluke "true RMS" meter, but the ones that I use at work are cheap, non-RMS types. "True RMS" capability only matters for AC voltages. It doesn't affect the DC ranges, normally. An ordinary, non-"true RMS" meter assumes that the AC voltage is a sinusoid. It measures the peak (or average rectified) voltage, and applies a correction factor to get RMS voltage. If the AC signal is a square wave, triangular wave, etc., then the correction factor that it uses will be wrong. The measured voltage will then be slightly incorrect. A "true RMS" meter uses more complicated circuitry to get a more accurate measurement, even when the AC waveform has an irregular shape.

A True RMS meter is useful when doing a lot of work with power line frequencies (50-60Hz), where the waveform may not be a sinusoid. It is not important to me, because an oscilloscope is better for measuring AC voltages anyway. In my opinion, it is better to get a cheap meter and a good used oscilloscope, rather than an expensive meter by itself.

The meter can be used to measure AC/DC current and voltage, resistance, and ideally capacitance and inductance. The oscilloscope can be used to measure both AC and DC voltages and frequency. It has the bonus that most of them can display two or four channels at the same time. An oscilloscope allows one to see the actual waveforms in a circuit, at two or four places at once.

I picked up an old Tektronix 547 oscilloscope, complete with the rolling cart, for $75. It was my first 'scope, and it still works today, although barely. There are much better models and deals to be had. Ebay has good deals, and bad ones. I don't know if you have "Ham radio" in your country, but if you do, local Hams can be very helpful with helping you find test equipment. Some may offer things for good deals, if you explain your situation and interests. If you post this question again in the thread, others will have some more useful advice to add.

Personally, I think the three very basic pieces of test equipment to have are a basic multi-meter, an oscilloscope, and a function signal generator.

I sometimes make mistakes, so it is better for others to be able to see what I'm writing, to provide "peer review" you know?

If you don't mind, I'll post this PM in the thread.

aga - 15-2-2015 at 14:26

When it comes to Tools, it always pays to get a Good one.

Bad tools cause all sorts of problems - even a Master Craftsman will struggle to make an artwork out of dog-turds.

For the price, a second hand Fluke 15B would be a good choice and last you decades.

jsc - 19-2-2015 at 07:29

Your multimeter was probably working correctly. You were probably doing something wrong. In that situation the right thing to do is to test it on a simple circuit, for example, 9v battery, resistor, LED. If you had put the meter in this circuit it probably would have shown the correct and expected current flow. Note that an ampmeter has to be inline with the circuit. You don't just touch the leads to the posts like with a voltage reading.

Modern "leadless" solder is difficult to work with. If you can find old leaded solder at a flea market I recommend that. Breadboards are a preferable alternative. Avoid soldering if at all possible.

Taking on a radio project is ambitious for a beginner and I would recommend starting off with much easier projects unless you have a definite and specific need to do radio. Also, radio is kind of a specialized field. Most "inventor" and "self-help" electronics projects deal with control and logic (turning stuff on and off), not radio.

I would not even attempt a radio project without a good quality LCR inductance meter. I use the DE-5000 LCR Meter which costs $140.

You cannot do radio projects on breadboards due to shielding and stray capacitance issues. Normally you do them what is called "dead bug" style.

Building a radio project out of a kit without understanding the theory of what is going on and just hoping to blindly duplicate someone else's design is not a recipe for success. Also, radio kits tend to be very simplified designs that are defective in many respects and do not work very well. When starting out, you want to be doing projects where the results are likely, definite and concrete.

If you are determined to do radio, I would recommend using Ronald Quan's book "Build Your Own Transistor Radios", which is light years ahead of anything else when it comes to practical radio tutorials. His designs are REAL working designs, not joke kits that don't work 90% of the time.

To learn starting from the ground up I would recommend the book "Complete Electronics Self-Teaching Guide" by Earl Boysen. This book goes step-by-step from the very beginning and teaches you all the basic stuff you need to know and how to use all the equipment. There are short exercises and problem sets for each section to test your understanding.

If you work through the 500 pages of Boysen's book, the next step would be "Electronics for Inventors" by Paul Scherz. This book has 1000 pages. This book goes into more practical details and outlines how to turn the theory and technique you learn in Boysen into real working projects that have a practical benefit. If you work through both of these books thoroughly, you will have a good working knowledge of how to do electronics.

[Edited on 19-2-2015 by jsc]

[Edited on 19-2-2015 by jsc]

Chemosynthesis - 19-2-2015 at 10:27

I wanted to extend a "thank you" for the book suggestions. Not only will they be helpful to me as well, but you gave me a great idea for a holiday present for a friend I know in avionics who was kind of disgusted at the quality of radio kits.

xfusion44 - 26-2-2015 at 22:29

To all of you, who are beginners in electronics, I'd suggest you to buy a good, but not too expensive soldering iron (some people just like to exaggerate with prices of equipment). For instance: 5$ soldering iron surely isn't very good for the job, but for 30-35$ you can get perfectly usable soldering station. It doesn't heat up in 10 seconds, but it's more than enough for beginners. If you really need soldering iron, that heats up in 10s, buy something for let's say up to 120$, but throwing money away on $500 Wellers is just nonsense. Personally I use cheap 30$ station, and at school I use $300 Weller and other than heating-up time, there's no benefits for Weller. Almost all you pay that "extra" for, is brand. The same with multimeters. I have 45$ Voltcraft multimeter, that has everything that beginner would ever need and more. Actually it's so good that I have the third one now. First one died because I've been measuring 4kV with it and it was only meant for 250V (CAT2). And somewhere I even have a picture of it with display reading of 2500V. Excellent multimeter and that's the proof, that you don't need to buy $100+ Flukes... Although Fluke is excellent brand, but if you're beginner, you don't need it. $40 multimeter will measure all of the basic stuff, like voltage AC/DC, current AC/DC (uA, mA and A must be separated), resistance, capacitor measurement, diode test, frequency, duty cycle, continuity test, non-contact voltage sensor (optionally). My VC175 is measuring up to 600V AC/DC (CAT3), which is very useful for higher voltages in switching circuits. Also, DO NOT buy cheap chinese multimeters as they can cause fire and can be very dangerous when using them on mains voltage. When buying multimeter also be sure, that it has HRC (high rupture capacity) fuses, which are much safer when it comes to overload.

[Edited on 27-2-2015 by xfusion44]

The Volatile Chemist - 3-3-2015 at 09:20

Indeed. I suggest something better than the $10 one too, as something shorted out in mine, and I'm yet to get another soldering iron.

radiance88 - 27-3-2015 at 20:33

Okay.. so I'm really stumped here. I am using another multimeter here, and have a simple circuit - a 1000 ohm resistor inbetween the 12v and 0 leads of my small transformer here. I have two wires connected in series with it which I use to measure my amperage.

No matter what I seem to do I can't ever get a good reading from it. Even when I hook up the leads from the DMM to it the DMM doesn't read anything but but slowly trails off down into zero as if it weren't even connected. I should be getting theoretically 12 mV.

Anyone have any ideas?

WGTR - 27-3-2015 at 21:27

I could be looking at it the wrong way, but it looks to me like the two red wires sticking in the air are both connected to the 0V side. There shouldn't be any measurable voltage or current there, since they are shorted together on the proto board.

aga - 28-3-2015 at 06:51

It does look that way.

On your breadboard, the connections are up/down for the middle two rows.

All of the others run left/right

Edit:

The holes in the breadboard in the photo are connected together like this :-

Central : all Xs are connected together, ditto all Ys
XY
XY
XY

All Others:

AAAAA BBBBB
CCCCC DDDDD
EEEEE FFFFF

They're like that so you can stick a DIL packaged chip in the middle and get to all the pins.

The up/down middle ones are like that so you can get power to all places easily.

[Edited on 28-3-2015 by aga]

The Volatile Chemist - 2-4-2015 at 11:22

That's funny. That's the same mistake I made when I first tried to use a breadboard. Or is it Bredboard? I've seen both...

aga - 2-4-2015 at 14:35

The Problem seems to be a basic misunderstanding of the Tools.

A simple circuit like a voltage source and a resistor cannot be this difficult.

Omit the Breadboard.

Use the twisting-together-of-wires method.

One of the wires from the transformer to one end of the resistor, twist together.
Ditto the other wire/the other end of the resistor.

Make sure there is a Voltage coming out of the transformer.
It will be AC not DC (set multimeter accordingly).

Oh dear.
To measure an AC Current you may need a different meter.

As you're just getting started, best use a DC source instead of an AC source.

First Project : build a DC voltage source.

You can just add a bridge rectifier to what you have : (search the page for Graetz bridge)

http://en.wikipedia.org/wiki/Rectifier

or use an old PC PSU instead (maybe cheaper)

http://www.instructables.com/id/How-To-Build-A-Power-Supply-...

m1tanker78 - 2-4-2015 at 17:42

Quote: Originally posted by radiance88

[...]have a simple circuit - a 1000 ohm resistor inbetween the 12v and 0 leads of my small transformer here. I have two wires connected in series with it which I use to measure my amperage.

No matter what I seem to do I can't ever get a good reading from it. Even when I hook up the leads from the DMM to it the DMM doesn't read anything but but slowly trails off down into zero as if it weren't even connected. I should be getting theoretically 12 mV.

Anyone have any ideas?

12mV is too little for your meter to resolve IMO. Try using a 100 ohm shunt to put you in the 100+mV ballpark. My DMM picks up 53mV of stray AC before zeroing without being connected to anything, for reference. AC (even switching DC for that matter) is kind of tricky to accurately measure. The problem is exaggerated in the tens of mV range and below.

Since you have a breadboard, you can rig up a simple and cheap bridge rectifier with '1n400x' diodes and try different capacitors for different loads. You can always simulate the circuit and then verify on the breadboard.

sodium_stearate - 20-4-2018 at 06:19

If you don't already have some, I highly recommend
getting some test leads.

These are also called clip leads. They come in 2 basic styles.
One style has small "mini-grabber" spring-loaded hooks
that are very handy for accessing small spaces such as
transistor or integrated circuit leads or pins.

The other type have alligator clips on the ends.

Having a huge wad of clip leads handy always makes
testing easy.

Also, I recommend making up a set of special leads
for your multimeter that plug into the holes on a
solderless breadboard.

You can easily make up a set of these meter leads.
One end will have an insulated female plug to push the meter
probe into. Then have that connected a short length
of #24 gauge tinned single-strand insulated copper wire
(make one red, the other black). Then on the far ends
of those leads, strip off about .25 inch of insulation
so the lead can fit down in any of the breadboard holes.

This makes using your multimeter on a solderless breadboard
circuit easy, safe, reliable, and completely painless.

One other thing: Regardless of what else you are told,
using anything larger in diameter than 24 gauge wire
in the solderless breadboard holes will stretch the tiny
springs open inside the solderless connectors down inside
the holes. Using #22 gauge wire will do this.

Once those tiny spring-contacts get stretched and bent open,
they make loose and flakey connections. That then leads
to all sorts of highly irritating intermittent problems with
any circuit built on the board.

To keep your solderless board fresh and tight, use only
24 gauge tinned jumpers. (not bare copper because that
oxidizes quickly, leading to more flakey connections)

Also I think that you need to obtain a copy of the
rather ancient hardcover book titled
"The Boy Electrician" by Alfred P. Morgan.

That book is very useful and it explains everything from
the ground up. It's not just for young boys either.
There are many projects in it that any adult will
find challenging and educational.

[Edited on 21-4-2018 by sodium_stearate]

mayko - 6-5-2018 at 17:06

for a long time, I had trouble soldering, even with a decent iron. In particular it was hard for me to keep the iron in contact with the component long enough to heat and melt properly without slipping off, and to compensate I was applying unnecessary pressure, which was a bad habit. All these problems went away when I used a chisel tip instead of the point type!

I dont't think that anyone has mentioned Forest Mims; here's a couple of his guides. I also have the Mims general electronics book but it's too large to attach ... if there's interest i'll look into hosting or something.

Attachment: Forrest Mims-engineer's mini-notebook 555 timer circuits (radio shack electronics).pdf (2.8MB)
This file has been downloaded 354 times

Attachment: Forrest Mims-Engineer's Mini-Notebook Magnet And Sensor Projects (Radio Shack Electronics).pdf (4.2MB)
This file has been downloaded 369 times

My first 555 project was based on the LED flasher on p. 26 of the Mims 555 book, a simple blinker with adjustable strobe rate:

I've also wanted to do some beefier projects like Tesla coils. I've been lugging around an old neon sign transformer since I found it a few years ago; only a recently did I get around to building a Jacob's Ladder with it. No mad science lab should be without!

IMG_20180423_jacobsLadderStuff.jpg - 266kB

sodium_stearate - 7-5-2018 at 04:35

Another thing that is never taught in schools
is that regular "rosin core" solder does not have enough
flux to make it really flow properly.

This lack of flow is mostly responsible for
many of the troubles people always seem to have
with soldering.

A plain plumber's flux that contains zinc chloride is
very good for most soldering jobs such as twisted wires,
soldering wires to terminal lugs and jobs like that.

That type of flux is somewhat conductive and so should
be avoided when soldering on any sort of printed circuit
board. Using this flux on a PC board will conduct some
small current across traces. (It will be in the k-ohms region)

So, for close work such as PC boards, a special non-conductive
flux must be used. The non-conductive flux is nowhere
near as good of a flux as the zinc chloride flux is.

That is why I keep, and use both kinds of flux.

When a solder joint is made on bright metal and with
the proper amount of flux, the solder flows freely
just like water, and it thoroughly wicks into all
tiny crevices.

Without enough flux, the solder gets all sticky and muddy
and it leaves annoying peaks and it does not flow
very good at all.

+1 on the flux

Sulaiman - 7-5-2018 at 05:23

For convenience I use a flux pen https://uk.rs-online.com/web/p/solder-fluxes/2513637/
I find it especially useful for smd as a little flux can be applied to the pads,
when allowed to evaporate for a few minutes it becomes sticky,
smd ICs can be tacked in place by pressing onto the sticky flux.

Even with added flux I use flux-cored solder (rosin has been discontinued for health reasons).
Lead-tin solder behaves much better than lead-free.
=================================
Regarding multimeters,
last year I bought an AN8002 multimeter that I am VERY pleased with,
others that I know bought the AN8008 and they are happy too.
https://www.ebay.co.uk/itm/Auto-Ranging-Digital-Multimeter-V...

DavidJR - 7-5-2018 at 07:11

Quote: Originally posted by Sulaiman

For convenience I use a flux pen https://uk.rs-online.com/web/p/solder-fluxes/2513637/
I find it especially useful for smd as a little flux can be applied to the pads,
when allowed to evaporate for a few minutes it becomes sticky,
smd ICs can be tacked in place by pressing onto the sticky flux.

Even with added flux I use flux-cored solder (rosin has been discontinued for health reasons).
Lead-tin solder behaves much better than lead-free.

I don't think it's entirely accurate to say 'rosin has been discontinued'. Sure, synthetic fluxes are increasingly common, but it's still easy to buy flux-cored solder as well as solder paste containing rosin/colophony.

Also, some of the newer lead-free alloys are not too terrible. Still, nothing beats 63/37 tin/lead (eutectic) solder.

yobbo II - 8-5-2018 at 04:02

How new and shiny your components and wires are will dictate how much solder and how aggressive the solder needs to be.
Brand new components that are clean and unhandled need very little. Old stuff that has been lying around for years needs very aggressive solder and lots of it. Maybe even clean with sandpaper ro steel wool.

sodium_stearate - 8-5-2018 at 17:57

The basic idea is to scrape off the oxidation layer
and get down to shiny copper. Solder will not
adhere to an oxide layer.

Also, I've never used the "new" "lead-free" solder
and never intend to use it. Everything I've heard
about it indicates that it's really lousy.

elementcollector1 - 8-5-2018 at 18:26

I've used lead-free solder on multiple occasions. It adheres significantly worse than lead-tin eutectic, but also doesn't smell bad and (presumably) doesn't cause lead poisoning to underpaid workers in Apple factories.

I'd recommend getting EagleCAD to those who want to invest their time in creating circuitboards - last I checked, it's free and does a ton of the work for you, including optimal path-generation.

mayko - 20-6-2018 at 09:56

Quote: Originally posted by mayko

I also have the Mims general electronics book but it's too large to attach ... if there's interest i'll look into hosting or something.

here it is anyway:

https://www.dropbox.com/s/r27ya2vjnq6j8o2/Radio%20Shack%20-%...

MJ101 - 20-6-2018 at 18:45

I'll throw my hat into the ring.

If you want to learn electronics, first understand DC circuits. Resistors, capacitors and inductors (chokes, transformers...) behave differently
with DC as opposed to AC.

Study up on Kirchoff's law,Thevenin and Norton's theorems.

Resistors are linear devices, and are governed by Ohm's law.

Take a look here: https://www.electronics-tutorials.ws/dccircuits/dcp_2.html

They are labelled with color bands that give you the value.

Here's a nice color band calculator, provided by DigiKey
https://www.digikey.com/en/resources/conversion-calculators/...

Both capacitors and inductors behave exponentially with DC; After roughly 5 time constants, a capacitor becomes an open circuit (Ideally)
An inductor becomes a short circuit after 5 time constants.

For capacitors: https://www.electronics-tutorials.ws/rc/rc_1.html

For inductors: https://www.electronics-tutorials.ws/inductor/lr-circuits.ht...

AC is a different story. Now we have reactance and resistance playing together.

For capacitors: https://www.electronics-tutorials.ws/capacitor/cap_8.html

For inductors: https://www.electronics-tutorials.ws/accircuits/ac-inductanc...

This seems to sum it up nicely
http://hades.mech.northwestern.edu/index.php/Resistors_(Ohm%27s_Law),_Capacitors,_and_Inductors

I would recommend that you invest in a good multimeter. I have a few of them lying around the bench.
If you're just starting out, get an inexpensive meter.

Just in case something goes wrong.

For parts, take a look at Joe Knows.
https://www.amazon.com/Joe-Knows-Electronics-Value-Resistor/...

ebay is also a good place to look, but you have to be careful. You could end up buying a lot of factory rejects. (Been there...done that)

For hand tools, that's up to you. I have an inexpensive set of pliers and cutters, and I have my precision tools.
I build guitar pedals as a hobby, so I build my prototypes with #28 gauge kynar wire wrap wire.

Take a look at erem tools. Some of the finest tools ever made. Also, look up weller xcelite. Top notch tools for servicing.

If you're going to build prototypes, invest in a temperature controlled soldering station. Too much heat is a nono, and can fry semiconductors.
Definitely worth the money.

If I can help, please let me know.

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